The present invention relates to injecting acid-wash into a subsea connection assembly, in particular for removing unwanted material.
Electric and hydraulic power, chemical injection and communications are typically transmitted to subsea wells via an umbilical from a surface or land based platform, the umbilical being terminated at an umbilical termination assembly (UTA). The feeds for electric and hydraulic power and chemical injection are effected from the UTA to a well tree, which houses a well control system, by a multiplicity of self-sealing individual connectors. In order to facilitate mating or unmating of the electric and hydraulic power and chemical injection connectors subsea by a remotely operated underwater vehicle (ROV), they are typically mounted together on a plate known as a stabplate, so that a single ROV action mates all the connectors. Such a stabplate arrangement is normally reserved for the electric and hydraulic power and chemical injection feeds to the well. The ROV locates the stabplate to a fixed reciprocal plate mounted on the subsea tree, and, typically, a screw mechanism is operated by the ROV to force the two plates to mate and to lock them together. The mating and locking screw mechanism is, typically, part of the stabplate connection and remains subsea during the operation of the well. Unmating of the stabplate connection for maintenance/repair purposes involves an operation by an ROV of unscrewing the screw mechanism, which is designed to force the mated plates apart.
Leaving the screw mechanism subsea for lengthy periods of time can result in corrosion and contamination (e.g. biological growths) which can cause the screw mechanism to seize. The result is either the need for other forceful methods of separating the stabplate from the fixed plate (invariably resulting in expensive damage to the well tree and parts of the stabplate connection) or the additional cost of including a secondary release mechanism in the design of the stabplate connection. A similar problem occurs with calcareous deposits formed in subsea structures employing cathodic protection (CP) systems. Because of this, the stabplate connection and sub-components are often liberally doused with sulphamic based or hydrochloric based acid wash to break down the deposits and growth and enable mating and de-mating of the hydraulic connectors.
The current technique applied by some stabplate connection vendors is to create a cavity around the fixed plate by boxing in the area between the stabplate and fixed plate in order to pass acid wash into this area via a connector on the stabplate. This approach is typically used on stabplate connections with a central screw-thread to mate/de-mate the plates. The disadvantage of this arrangement is that this means a specific design must be used for such applications, with the extra cost and mass involved in the extra material. Furthermore, this means an ROV needs to make up a hot-stab (i.e. a high pressure subsea quick dis-connector) with every stabplate to deploy the acid-wash.
However, modern improvements to stabplate design, e.g. the design disclosed in GB-A-2473444, allow for the removal of the central mating and locking screw mechanism (which additionally provides the benefit of removing part of the mechanism which is prone to calcareous deposit) and thus after mating leaving a central opening in the stabplate connection. This central opening permits application of the present invention, which removes the disadvantages of existing systems detailed above, and provides a much more directed and efficient acid application to remove deposits and growths.